Overview of the inelastic neutron scattering intensities of CrCl\(_3\)  at \(T\)  = 4 K is displayed in Fig. REF (d). Strong and dispersive excitations are observed at low energies below \(E \le \)  9 meV, whose intensity decreases at larger wave vectors (\(Q\) ) indicating that these are magnetic excitations. These excitations consist of two bands separated at \(\sim \)  4 meV, which are ascribed to the two sublattice spins of a simple honeycomb lattice. The upper and lower bands account for in-phase and out-of-phase precessions, respectively, of the two sublattice spins. Additional intensities observed at high energies, \(E \approx \)  14.5 and 17.5 meV, are ascribed to phonon excitations as they increase in intensity at higher wave vectors. These energies are also consistent with recent Raman scattering observations of phonon signals at \(\sim \)  115 and 140 cm\(^{-1}\)  [1]}, [2]}.
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